The present invention relates to the field of metallic fasteners. More specifically, the present invention relates to the field of drive pins for attachment of material to sheet metal.
There exists a need to fasten material to a relatively thin (i.e., sheet) metal substrate. This need may be typified by the fastening of cladding or sheathing material to structural steel framing members, the fastening of components to metal tubing or structural forms, etc. This need is typically fulfilled by welding, brazing, gluing, riveting, screwing, or pinning.
When the material to be fastened is another metal, welding or brazing is often used. These fastening methods have the advantage of strength and component cost. Welding and brazing are clean, fast and efficient when used in automated assembly operations. This may be seen in the construction of automobile bodies and frames on robotic assembly lines. When manual fastening is required, as in field construction, welding and brazing become time-consuming and labor intensive.
Under certain low-stress conditions, a suitable construction adhesive may be used to fasten a material to a metal substrate. Such assemblies typically require a high degree of conformity between the material and the substrate. For example, to be successfully glued to a framing member, the surface of a rigid sheet material must lie flush to the surface of the framing member. Even a small misalignment may result in a poor bond. For these and other reasons, gluing is restricted to specific forms of construction and is generally not practical in the field.
Riveting, screwing, and pinning are generally the methods of choice for fastening materials in the field. Each of these methods has its strengths and weaknesses. Riveting typically requires access to both sides of the join, i.e., to the xe2x80x9cfacexe2x80x9d of the material and the xe2x80x9cbackxe2x80x9d of the metal substrate. This is not always practical, nor always possible. Additionally, a rivet is a double-headed fastener, having one head preformed and the second head formed in situ. This is typically a forceful operation. The force needed to deform of the tip of the rivet to form the second head would generally deform a thin metal substrate. Riveting is therefore generally limited to the thicker metals.
Screwing and bolting may be used with materials of virtually any thickness. Bolting, i.e., the use of a bolt with a nut, provides a very strong bond. Bolting is also repeatable, i.e., the material may be repeatedly attached and removed from the substrate as required. This makes bolting the method of choice where either extreme strength or removability is desired. However, bolting typically requires pre-drilled holes, two fasteners (the bolt and the nut), and is labor intensive. Bolting is therefore time consuming and expensive. Bolting may also require access to both sides of the join, thereby limiting its practicality.
A single-fastener variant of bolting may be used where a hole is pre-drilled and threaded in the metal substrate, thereby serving as the nut. Alternatively, in lieu of a tapped hole, a nut may be pre-positioned at a pre-drilled hole in the metal substrate by any of a plurality of methods (e.g., welds, recesses, clips, etc.) well known to those skilled in the art. Since the xe2x80x9cnutxe2x80x9d is in place, only the bolt need be used to fasten a material to the metal substrate and access to both sides of the join is not required. This significantly improves in-field efficiency. Unfortunately, overall efficiency is reduced and costs increased by the requisite pre-processing, i.e., drilling and tapping of the substrate and/or affixment of the nuts. The tapped-hole bolting method is also not generally practical for thin metal substrates, e.g., those of less than 0.125 inch.
For thin metal substrates, significant installation efficiency over bolting may be realized by screwing the material to the metal substrate. Self-tapping screws cut their own threads in metal substrates with pre-drilled holes. Self-drilling screws eliminate the need for pre-drilled holes. Each of these screws may be used to rapidly and efficiently fasten the material to the substrate in the field.
Self-drilling screws drill their own holes in the material and the metal substrate. This makes them ideal for field installation of drywall, sheathing, and general framing applications. The use of self-drilling screws is especially efficient when such screws are used with an automatic (i.e., pneumatic or electric) screw gun.
Pinning presents the most efficient method, from a labor and time perspective, of fastening a material to a thin metal substrate. In this method, a drive pin percussively penetrates the material and the metal substrate by an automatic (pneumatic, electric, fuel cell, or powder-actuated) nailer. Since most automatic nailers use drive pins that are belt, coil, or strip fed, an operation such as attaching gypsum sheathing to steel framing becomes rapid and efficient. Only a fraction of a second is required to drive each drive pin in a sheet of material. This is a marked improvement over screwing, where a few seconds per screw is required.
A disadvantage of pinning is that it conventionally has less holding power than screwing. This makes pinning less desirable where great strength is needed. This is especially true of pullout resistance or grip (i.e., strength in a direction perpendicular to the material surface). The grip of a pinned join (assuming a proper fastening operation) is a function of the thickness and material of the metal substrate, and the dimensions and configuration of the drive pin.
Conventional drive pins are fluted to increase grip. That is, they have grooves and ridges upon their shanks configured to deform upon use to strengthen the join. These fluted-shank pins may have either straight or spiraled grooves. Straight grooves are conventionally used with thicker metal substrates where a wedging action between the pin and the substrate contributes to the strength of the join. Such straight-fluted pins do not produce desirable joins with thin substrates, e.g., conventional steel framing members.
For thin substrates, i.e., less than 0.25 inch, a spirally fluted drive pin, also known as a drive screw, is preferred. The drive pin is configured to penetrate the material and the metal substrate. To accomplish this, the drive pin conventionally has a ballistic (i.e., bullet-shaped) tip configured to pierce the substrate and create an opening therein substantially equal to the diameter of the shank. The spiral flutes, i.e., the groves and ridges, then spin the drive pin while substantially simultaneously cutting threads into the substrate and deforming to lock the drive pin therein. It has been found that, under normal conditions, thicker metal substrates require shallower twist angles, as the thicker material imposes a greater resistance to the spinning of the drive pin.
Typically, the spiral flutes subtend an angle of approximately ten degrees relative to an axis of the shank. These conventional ten-degree-spiral drive pins work well for thicker sheet-metal substrates, e.g., those thicker than approximately 10 gauge (0.1180 inch). Such thicknesses may be found on shipping containers, for which the drive pins were first developed, and other high-stress applications. For the thinner gauge sheet-metal framing members typically used on commercial and residential buildings, i.e., 12 to 25 gauge (0.0966 to 0.0179 inch) the performance rapidly decreases.
Because the conventional drive pin was developed for use with thicker metal substrates, certain concessions in pin design have become common in the industry. One such concession is the use of truncated or flattened threads. In such pins, the ridge in the groove-and-ridge arrangement is formed with a flat top. This truncation reduces the number of fine chips torn from the spiral ridges during the impact fastening operation. Few fine chips result in an increase in average chip size. The larger chips act as better wedges, thereby providing a better grip in thicker substrates. In thinner substrates, however, this truncation results in less of a thread being cut into the substrate. Since it is the depth and quality of the thread that provides the grip with thinner substrates, a reduction in thread depth and quality results in a lessened grip.
Several attempts have been made to produce a drive pin with increased grip in the thinner sheet metals. The most successful of which is the use of spiral flutes cut with annular rings. The annular rings cut the thin metal more cleanly, thereby increasing the quality of the threads and improving the grip. Unfortunately, this approach offers only marginal improvement when used with the thinnest sheet metals, i.e., 18 to 25 gauge (0.0428 to 0.0179 inch), often used for framing members in light commercial and residential construction.
Additionally, steel is often recycled. The makeup of virgin (new) steel can be controlled to very close tolerances. This means that virgin steel is substantially homogeneous, having the same balance of iron, carbon, and other materials throughout. This is not always true of recycled steel. Recycled steel may have spots or areas containing more or less carbon and/or other materials than iron. These spots may vary widely in hardness, resulting in brittle areas and soft areas in the same material. Since lightweight structural framing members are often produced from recycled steel, conventional drive pins have problems providing sufficient grip in all cases.
Accordingly, it is an advantage of the present invention that a drive pin for fastening a material to a metal base member is provided.
It is another advantage of the present invention that a drive pin is provided that is configured specifically for thin structural framing members.
It is another advantage of the present invention that a drive pin is provided that provides good grip in framing members of varying thicknesses.
It is another advantage of the present invention that a drive pin is provided that provides good grip in a framing member having varying hardness.
It is another advantage of the present invention that a drive pin is provided that provides a thread formed full upon the shank.
The above and other advantages of the present invention are carried out in one form by a drive pin for the fastening of a material to a metal base member with an automatic nailer. The drive pin has a head, a substantially cylindrical shank upon which a knurl is rolled having a plurality of substantially parallel spiral grooves, each groove subtending an angle of at least 15 degrees relative to an axis of the shank, and a ballistic tip configured to penetrate the material and the metal base member under force of the automatic nailer.